Cyclopentadienyl-containing low-valent early transition metal olefin polymerization catalysts

ABSTRACT

A catalyst system useful to polymerize and co-polymerize polar and non-polar olefin monomers is formed by in situ reduction with a reducing agent of a catalyst precursor comprising 
 
{Cp*MRR′ n } + {A} − 
 
wherein Cp* is a cyclopentadienyl or substituted cyclopentadienyl moiety; M is an early transition metal; R is a C 1 -C 20  hydrocarbyl; R′ are independently selected from hydride, C 1 -C 20  hydrocarbyl, SiR″ 3 , NR″ 2 , OR″, SR″, GeR″ 3 , SnR″ 3 , and C═C groups (R″=C 1 -C 10  hydrocarbyl); n is an integer selected to balance the oxidation state of M; and A is a suitable non-coordinating anionic cocatalyst or precursor. This catalyst system may form stereoregular olefin polymers including syndiotactic polymers of styrene and methylmethacrylate and isotactic copolymers of polar and nonpolar olefin monomers such as methylmethacrylate and styrene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/142,329, filed Jul. 3, 1999, which is incorporated by referenceherein.

STATEMENT REGARDING FEDERALLV SPONSORED RESEARCH OR DEVELOPMENT

This invention, in part, was made with Government support under GrantNo. 86 ER 13511 awarded by the United States Department of Energy. TheUnited States Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION

This invention relates to a cylcopentadienyl-containing low-valenttransition metal catalyst that is useful in polymerizing andco-polymerizing polar and non-polar olefin monomers, and moreparticularly relates to an in situ reduced Group 4 metal polymerizationcatalyst that is capable of forming polymers and copolymers ofconjugated monomers such as methyl methacrylate (MMA) and styrene.

Catalysts based on early transition metal d⁰ complexes, such asZiegler-Natta catalysts, are used extensively for coordinationpolymerization of nonpolar olefins such as ethylene and propylene.However, due to their highly oxophilic nature, these catalysts typicallyare incompatible with functionalized vinyl monomers in achieving eitherinsertive polymerization of polar olefins or copolymerization ofnonpolar olefins with polar comonomers.

Late transition metal catalysts are less oxophilic; however, most oftenthey effect olefin dimerization or oligomerization rather thanpolymerization to high molecular weight polymers. Recently, Brookhartand co-workers (J. Am. Chem. Soc., 1996, 118, 267-268) reported examplesof late transition metal-catalyzed insertive copolymerizations ofnonpolar olefins (ethylene and propylene) with alkyl acrylates to givehigh molar mass (high molecular weight) polymers. However, activitiesbecome significantly lower as the polar comonomer concentrationincreases and polar groups are only detected at the end of polymer chainbranches. Polymerization of olefins containing functional groups in aposition remote from the vinyl group by early transition metal catalystshas been reported as have been very oxophilic catalysts such aslanthanocene and zirconocene to catalyze polymerization of polarmonomers such as MMA or lactones through a Michael addition mechanism.

Crystalline vinyl aromatic polymers such as syndiotactic polystyrenehave been produced from single-site or metallocene catalysts. EP 0 421659 describes production of syndiotactic polystyrene using amono-cyclopentadienyl complexed transition metal catalyst in combinationwith a non-coordinating anion such as a perfluoro borane or borate.

Polymers of polar vinyl monomers, such as MMA, are well known andtypically are produced through a radical polymerization mechanism.Radical polymerization processes may have high polymerization activityfor functionalized olefins, but usually require high pressure, producebroad molecular weight distribution resins, and do not controlstereoregularity. Single-site catalysts, such as those based on acylcopentadienyl ligand complexed with a transition metal, polymerizeolefins with controllable molecular weights and stereoregularity andwith narrow molecular weight distributions. However, these single-sitecatalysts typically do not polymerize functionalized olefins orcopolymerize a functionalized with non-functionalized olefins.

Copolymerization of polar monomers with olefins using transition metalcomplexes is reviewed by Boffa and Novak, Chem. Rev. 2000, 100,1479-1493, incorporated by reference herein.

Soga et al., Macromolecules, 1994, 27, 7938-7940, report formation of asyndio-rich atactic polymer of MMA using a metallocene cationic complexCp₂Zr(CH₃)⁺B(C₆F₅)₄ ⁻ in toluene in the required presence of diethylzinc. Also, Chen et al. J. Am. Chem. Soc., 1998, 120, 6287-6305,incorporated herein by reference, reported MMA polymerization using abinuclear {Cp₂Zr(CH₃)}₂CH₃ ⁺-type catalyst using a living group transferprocess mechanism and not coordinative polymerization.

U.S. Pat. No. 5,616,748 describes formation of a neutral reduced metaltitanium cyclopentadienyl complex using a lithium alkyl reducing agent,but does not describe combinations with non-coordinating anions or useas a polymerization catalyst for polar and nonpolar olefins.

Our invention relates to a catalyst system that is capable ofpolymerizing polar and non-polar olefins. Examples of polar/nonpolarcopolymers may be stereoregular as well as containing regions ofalternating monomer polar/nonpolar units.

In one aspect of this invention, a monocyclopentadienyl transition metalmetallocene combined with a non-coordinating cocatalyst anion is reducedin situ with a suitable reducing agent such as zinc metal to form anactive olefin polymerization catalyst system capable of polymerizing andcopolymerizing both polar and nonpolar olefins.

In another aspect of this invention, a monocylcopentadienyl-containingGroup 4 metal complex in combination with a non-coordinating borateanion is reduced in situ with a metallic reducing agent such as zinc toform an active olefin polymerization catalyst.

In another aspect of the invention, stereoregular copolymers of polarand nonpolar olefins are formed. In other aspect of the inventionstyrene and methylmethacrylate are polymerized to crystalline polymersand copolymerized to isotactic copolymers containing 10 mol % or more ofmethylmethacrylate monomer units. These and other aspects of thisinvention are described and claimed herein.

Polar copolymers generally are useful as barrier materials forpackaging; have improved adhesioin/paintability/wetabilitycharacteristics; have functionalization points for grafting, coating,and lamination; may be blend compatibilizers for multilayeredstructures; may be a replacement for halogen-coating polymers, and haveimproved processing and mechanical properties.

SUMMARY OF THE INVENTION

A catalyst system useful to polymerize and co-polymerize polar andnon-polar olefin monomers is formed by in situ reduction with a reducingagent of a catalyst precursor comprising{Cp*MRR′_(n)}⁺{A}⁻wherein Cp* is a cyclopentadienyl or substituted cyclopentadienylmoiety; M is an early transition metal; R is a C₁-C₂₀ hydrocarbyl; R′are independently selected from hydride, C₁-C₂₀ hydrocarbyl, SiR″₃,NR″₂, OR″, SR″, GeR″₃, SnR″₃, and C═C groups (R″=C₁-C₁₀ hydrocarbyl); nis an integer selected to balance the oxidation state of M; and A is asuitable non-coordinating anionic cocatalyst or precursor. This catalystsystem may form stereoregular olefin polymers including syndiotacticpolymers of styrene and methylmethacrylate and isotactic copolymers ofpolar and nonpolar olefin monomers such as methylmethacrylate andstyrene.

DESCRIPTION OF THE INVENTION

This invention describes early transition metal catalyst systems thatare capable of polymerizing and co-polymerizing olefin-containingmonomers which may be polar or nonpolar. These catalyst systems combinean ability to polymerize monomers in a stereoregular manner by anapparent insertive polymerization mechanism with a stabilization of thenormal oxophilic character of early transition metal catalysts to permitpolymerization of polar monomers. Also these catalyst systems maypolymerize olefin monomers that are functionalized with polar groupsthat typically poison conventional early transition metal catalysts.

It is believed that at least for many polymerizations described in thisinvention, an intermediate is formed containing the transition metalspecies and an olefin polymer chain into which olefin monomer inserts toextend the polymer chain. This “insertive” polymerization typicallyforms stereospecific polymers. For example, homopolymerization of apolar monomer such as MMA according to this invention typically willform syndiotactic polymer, and copolymerization of a polar and nonpolarmonomers (e.g., MMA and styrene) forms co-isotactic copolymers. As usedfor this invention, syndiotactic polymer refers to a polyolefin backbonepolymer with a majority of substituents in alternating stereopositions.Such syndiotactic stereo microstructure is observed as racemic (r)triads in ¹³C nuclear magnetic resonance (NMR) spectroscopy. In anisotactic (or, for a copolymer, a co-isotactic) polymer, the majority ofsubstituents are located in one stereoposition and this microstructureis observed as meso (m) triads in ¹³C NMR spectroscopy.

The catalyst systems of this invention are based on an in situ reducedlow-valent monocyclopentadienyl complex that does not exhibit asufficient oxophilic character to prevent polar monomer polymerization.Useful catalyst systems include early transition metal materials thathave been charge balanced with a suitable anionic co-catalyst andreduced to a lower oxidation state using a suitable reducing agent.

As used in this invention, a transition metal is complexed with acyclopentadienyl moiety to form a catalyst precursor. Preferably, aneutral transition metal precursor is complexed with a cylcopentadienylstructure represented as:Cp*MRR′_(n)wherein Cp* is a cyclopentadienyl or substituted cyclopentadienylmoiety; M is an early transition metal such as a Group 4 transitionmetal; R is a C₁-C₂₀ hydrocarbyl substituent suitable for insertivepolymerization; R′ are independently selected from hydride, C₁-C₂₀hydrocarbyl, SiR₃, NR₁₂, OR″, SR″, GeR″₃, and SnR″₃, and C═C groups withR″=C₁-C₁₀ hydrocarbyl; and n is an integer selected to balance theoxidation state of M.

In this invention, hydrocarbyl groups include alkyl, aryl, alkylaryl,arylalkyl, and alkenyl (such as vinylic) groups, and further may becyclic or acyclic.

Early transition metals include Groups 3, 4, 5, and 6 (new IUPACnomenclature) and lanthanide metals and particularly include Group 4metal species (e.g., titanium, zirconium, and hafnium) with titanium inthe +4 formal oxidation state (Ti^(IV)) as the preferred transitionmetal useful in this invention.

For the preferable Group 4 transition metal, such as titanium, in the +4formal oxidation state, a neutral transition metal precursor iscomplexed with a cylcopentadienyl structure represented as:Cp*MRR′₂wherein Cp, R, R′ are as defined above.

To form the catalyst system of this invention, a precursor is formed byreaction with a non-coordinating co-catalyst (A) to form a Cp*M cationcharge balanced with the co-catalyst anion to form a catalyst precursorstructure represented as:{Cp*MRR′_(n)}⁺{A}⁻wherein Cp* is a cyclopentadienyl or substituted cyclopentadienylmoiety; M is an early transition metal; R is a C₁-C₂₀ hydrocarbyl; R′are independently selected from hydride, C₁-C₂₀ hydrocarbyl, SiR₃, NR″₂,OR″, SR″, GeR″₃, SnR″₃ and C═C groups (R″=C₁-C₁₀ hydrocarbyl); n is aninteger selected to balance the oxidation state of M; and A is asuitable non-coordinating anionic cocatalyst.

Typically, a Group 4 transition metal Cp*M complex is reacted with anon-coordinating co-catalyst (A) to form a Cp*M cation charge balancedwith the co-catalyst anion to form a catalyst precursor structurerepresented as:{Cp*M^(IV)RR′}⁺{A}⁻

To produce the catalyst systems useful in this invention, theCp-containing catalyst precursor is reduced with a reducing agent insitu to form what is believed to be a Cp*M complex containing atransition metal that has been reduced from its highest oxidation stateto form a complex capable of polymerizing olefins.

A preferable catalyst precursor includes Ti^(IV) with R and R′ selectedas methyl, as represented below:{Cp*Ti^(IV)Me₂}⁺{A}⁻

If the transition metal is titanium, the substituent R is methyl, andthe reducing agent is zinc metal, resulting complex (assumed to beCp*Ti^(III)) may be formed according to the following proposed reactionscheme:

In more detail, early transition metals useful in this inventionpreferably are Group 4 metals and most preferably titanium. As used inthis invention, Cp* is a cyclopentadienyl or substitutedcyclopentadienyl group capable of forming a complex with an earlytransition metal. There may be up to five independently selectedsubstituents per cyclopentadienyl moiety. Substituents onto thecyclopentadienyl may include C₁-C₂₀ alkyl or aryl groups, which may beacyclic or cyclic, together with compatible heteroatom-containing groupssuch as groups containing silicon, nitrogen, and phosphorus.Substituents may be alkyl such as methyl, ethyl, propyl, isopropyl,butyl and the like; or aryl such as phenyl or a phenyl substituted withone or more alkyl or aryl groups; or an alkyl substituted with arylgroups. Substituted cyclopentadienyl groups may form cyclic structuressuch as indenyl or fluorenyl which also may be substituted with similarcompatible groups. A preferable Cp* is cyclopentadienyl.

Substituents (R and R′) on the Cp*M complex preferably are C₁-C₂₀hydrocarbons and most preferably C₁-C₄ hydrocarbyl. Since the mostpreferred substituent in the final catalyst system material is methyl,preferably at least one substituent in the precursor complexes is methylor a substituent which may be replaced by methyl during the catalystformation process. For example, if the initial substituent on thetransition metal is a halide such as chloride, reaction with a MAO orMMAO cocatalyst typically exchanges the halide to methyl as part of theactivation process.

Co-catalysts useful in this invention typically are selected fromnon-coordinating anions or precursors thereof. A non-coordinating anionwill balance the charge of a transition metal-containing cation, butwill not react with the cation to form a separate neutral species. Thus,the non-coordinating anion will be displaced during polymer formation.

Typically suitable co-catalysts include boron-containing materials suchas borates and boranes, and particularly include perfluoro substitutedborates and boranes. Other suitable co-catalysts may be formed fromaluminate species. Perflluoroarylboranes, such astris(pentafluorophenyl)borane, B(C₆F₅)₃ (FAB), tris(2,2′,2″-nonafluorbiphenyl)borane (PBB), tris(β-perfluoronaphthyl)borane(PNB) are preferable co-catalyst anion precursors. The most preferableperfluoroarylboranes cocatalyst precursor is PBB. Although usually notpreferred in this for the catalyst systems of this invention, use ofmethylaluminoxane (MAO) or modified methylaluminoxane (MMAO) as aco-catalyst typically converts a halide substituent in a Cp* complex tothe preferred methyl group substituent. Borate salts also may be used ascocatalysts such as trityl (Ph₃C+) salts of perfluorophenyl borates. Avariety of suitable cocatalysts are described by Chen and Marks, Chem.Rev. 2000, 100, 1391-1434, incorporated by reference herein.

Oxygen or water scavengers including aluminum alkyls such astriisobutylaluminum may be used in combination with the catalyst systemsof this invention.

Although Cp*T^(III) is believed to be formed in the catalyst systems ofthis invention, it was found that the Ti^(III) compounds, CP*Ti^(III)Me₂and CpTi^(III)(CH₂Ph)₂, are unstable in solution at room temperaturewithout the presence of a co-catalyst during reduction. As soon as acocatalyst such as MAO, B(C₆F₅)₃, PBB, or Ph₃C⁺B(C₆F₅)₄ ⁻ is added to apreformed Ti^(III) compound, decomposition occurs immediately even inthe presence of Zn, and the solution obtained displays no catalyticactivity for MMA or styrene polymerization. Thus, in a preferred methodto produce the catalyst system of this invention, a neutral transitionmetal metallocene precursor, such as Cp*TiMe₃ is reacted with acocatalyst, such as trityl perfluorophenyl borate (Ph₃C⁺B(C₆F₅)₄ ⁻),either prior to, or simultaneously with, contact with a reducing agentsuch as zinc metal. Either procedure is considered to be an in situreduction of a metallocene/anionic co-catalyst precursor according tothis invention. Typically, the reaction of the metallocene precursorwith the co-catalyst occurs in a suitable solvent or diluent that,preferably, is inert to the reactants. A suitable liquid diluent istoluene, although other hydrocarbons or substituted hydrocarbons may beused.

The in situ reduction of the metallocene/anionic co-catalyst precursortypically is performed at ambient temperatures, but may be conducted atany temperature at which the reduction occurs at a reasonable rate andat which the reactants and products are stable. Typical reductiontemperatures are from about 0 to 50° C. and normally are about 15 to 30°C. Reaction times may range from a few minutes to a few hours andtypically are from about 30 minutes to about three hours. The in situ 10reduction may occur in an diluent or solvent such as toluene or otherliquid hydrocarbon or substituted hydrocarbon.

Suitable reducing agents typically are metals or metal alloys that arecapable of reducing a transition metal to a lower oxidation state andparticularly of reducing a Group 4 transition metal in a +4 oxidationstate to a lower (e.g., +3) oxidation state. The preferable metallicreducing agent useful in this invention is zinc metal which typically isin the form of a fine powder. Other reducing agents include Zn—Cu,Zn—Ag, Mg, Ca, Na, Sn, Na/Hg, K/Hg, and Mg/Hg. Other materialsconsidered in this invention to be suitable reducing agents of thisinvention are alkali or alkaline earth metal aromatic salts such as Na⁺A⁻ and Mg⁺²Ar⁻², where Ar is an aromatic moiety. Although the reducingagent, such as zinc is necessary to stabilize the catalyst system duringreduction, it has been observed that presence of the reducing agent isnot necessary during polymerization.

In catalyst systems of this invention, the {Cp*Ti^(III)Me}⁺ moietyformed is very open sterically and thus favors binding of functionalizedolefins to the metal center through what is believed to be η⁴coordination (avoiding catalyst poisoning as shown in Eq. 1),

whereas more crowded {Cp′Ti(X)Me}⁺ type (e.g., X=Cp′, {Cp′₂TiMe}⁺; X=Me,{Cp′TiMe₂}⁺; or X=N(^(t)Bu), {CGCTiMe}⁺) structures are not as suitablefor multiple η⁴ MMA binding.

The Ti^(III) compound, Cp*Ti^(III)Cl₂, activated with MAO in thepresence of Zn is active for MMA polymerization but produces anamorphous poly(methylmethacrylate) (a-PMMA). Polymerization of MMA orcopolymerization of styrene with MMA catalyzed by this catalyst is muchslower than by the Cp*TiMe₃/Ph₃C⁺B(C₆F₅)₄ ⁻/Zn system of this inventionand does not produce isotactic (co-iso) copolymer product.

The catalysts of this invention may produce both homopolymers andcopolymers of polar and nonpolar monomers. According to this invention,copolymers are polymers containing more than one monomer and includeterpolymers. A particularly useful copolymer of this invention containsa nonpolar monomer such as styrene and a polar monomer such as MMA.

Monomers useful to form the polymers and copolymers of this inventioninclude both polar and nonpolar olefin species containing from 2 toabout 20 carbon atoms. Typically, polar monomers contain other atomssuch as oxygen, nitrogen, sulfur, and halides in addition to an olefiniccarbon-carbon double bond. The most typical polar monomers containoxygen or nitrogen such as unsaturated acids including acrylic acid,methacrylic acid, and their derivatives such as acrylates (e.g.,methylmethacrylate (MMA) methyl acrylate, butyl acrylate, and butylmethacrylate); vinyl esters (e.g., vinyl acetate, methyl 3-butenonate,methyl 4-pentenoate); unsaturated anhydrides (e.g., maleic anhydride;succinic anhydride); vinyl chloride; vinyl amides; vinyl amines;acrylonitrile; polar group functionalized norbornenes, and the like.Other examples of polar monomers include α,β-unsaturated carbonylcompounds such as carboxylic acids, anhydrides and esters, amides andketones. A preferable polar monomer used in this invention is MMA.

Suitable nonpolar olefins include ethylene and alpha-olefins (e.g.,propylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene-1,1-heptene,1-octene, 1-nonene, 1-decene, and the like); internal olefins (e.g.,2-butene); and cyclic olefins (e.g., cyclopentene, cyclohexene,norbornene, and the like); together with dienes (e.g., butadiene,isoprene, 1,5-hexadiene, and the like). Preferable non-polar olefinsinclude C₄-C₂₀ conjugated dienes such as butadiene and isoprene;aromatic vinyl species such as styrene and divinyl benzene; norbornene;together with alkyl and aryl substituted derivatives thereof. Apreferable nonpolar monomer used in this invention is a vinyl aromaticand preferably is styrene.

Catalyst preparation according to this invention should be underoxygen-free and water-free conditions as known in the art. Also,transfer of catalyst to a polymerization reactor should be carried outin an oxygen-free and water-free environment. Monomers used inpolymerization should be purified to the extent necessary to removedetrimental contaminants known to the art such as oxygen, water,sulfides, and the like.

The catalysts of this invention may be used directly in solution orslurry polymerization systems. If desired, the catalysts may besupported onto inert materials such as silica, alumina, orsilica/alumina as known in the art. Supported catalyst systems arepreferable in bulk and gas-phase polymerization techniques.

Typically, sufficient amounts of catalyst or catalyst component are usedfor the reactor system and process conditions selected. In apolymerization according to this invention, a measured quantity ofcatalyst material in a solvent or suspension is introduced in acontrolled manner to a polymerization vessel. The amount of catalystwill depend upon the activity of the specific catalyst chosen.

Irrespective of the polymerization or copolymerization process employed,polymerization or copolymerization should be carried out at temperaturessufficiently high to ensure reasonable polymerization orcopolymerization rates and avoid unduly long reactor residence times,but not so high as to cause catalyst deactivation or polymerdegradation. Generally, temperatures range from about 0° to about 120°C. with a range of from about 20° C. to about 95° C. being preferredfrom the standpoint of attaining good catalyst performance and highproduction rates. A preferable polymerization range according to thisinvention is about 50° C. to about 80° C.

Olefin polymerization or copolymerization according to this invention iscarried out at monomer pressures of about atmospheric or above.Generally, monomer pressures range from about 20 to about 600 psi (140to 4100 kPa), although in vapor phase polymerizations orcopolymerizations, monomer pressures should not be below the vaporpressure at the polymerization or copolymerization temperature of thealpha-olefin to be polymerized or copolymerized.

The polymerization or copolymerization time will generally range fromabout ½ to several hours in batch processes with corresponding averageresidence times in continuous processes. Polymerization orcopolymerization times ranging from about 1 to about 4 hours are typicalin autoclave-type reactions. In slurry processes, the polymerization orcopolymerization time can be regulated as desired. Polymerization orcopolymerization times ranging from about ½ to several hours aregenerally sufficient in continuous slurry processes.

Monomer structures also are important for polymerization andcopolymerization. Except for MMA and styrene, other monomers withconjugation such as butadiene and isoprene also are active, whereasmonomers without conjugation susceptible to classical cationicpolymerization processes such as vinyl ether and vinyl acetate typicallyare not active. This observation indicates that the polymerization doesnot proceed by a classical cationic pathway. GPC-derived weight averagemolecular weight (M_(w)) and molecular weight distribution (M_(w)/M_(n))data for PMMA, PS, and copolymers obtained using the present catalystsalso indicate typical single site Ziegler-Natta catalyzed copolymerproducts. Based on these observations and the ¹H NMR end-group analysisfor both homopolymer and copolymer products, a 2,1-insertion mechanisticpolymerization scheme can be proposed for the present systems (Eqs. 2-1and 2-2, below). It is believed that syndio- or co-iso-regulation comesfrom the prohibited insertion of head-to-tail monomer binding. Detectionof minimal or no 1,2-insertion product (polymer chains with terminal endgroups) is a evidence of η⁴ monomer binding because such a 1,2-insertionis blocked by the second coordinated double bond, such as C═O for MMA orη² Ph for styrene.

Via 2,1-Insertion Pathway Chain End with an Internal Vinyl Group

Via 1,2-Insertion Pathway Chain End with a Terminal Vinyl Group(P=polymer chain; For styrene: R=H, R1=phenyl; For MMA: R=Me, R1=COOMe)

NMR analysis of the polymer chain end groups (400 MHz, 21° C., intoluene-d₈) shows a chemical shift (6) of 6.03 for syndiotacticpolystyrene (s-PS) and δ 6.35 for syndiotactic poly-MMA (s-PMMA)corresponding to the internal vinyl end group proton chemical shifts. Noterminal vinyl end groups (−64.8) are detected for either indicatingless than 1 mol % present. This indicates that both s-PMMA and s-PS areproduced via 2,1-insertion (Eq. 2), not via 1,2-insertion (Eq. 3). TheMMA homopolymer with internal vinyl end groups is reported here for thefirst time.

MMA polymerization rates are slightly higher than those of styrene asobserved in Examples 1 and 2. With a 1:1 MMA:styrene feed ratio, largeamounts of s-PMMA are obtained instead of copolymer (Example 3) which isconsistent with a faster rate of MMA polymerization. This results in thedecrease of MMA concentration with increasing reaction times. Thus, in atypical polymerization, copolymers of differing incorporated MMA tostyrene ratios are produced. High MMA incorporated copolymer can beobtained by limited conversion procedures, and the MMA percentageincorporation can be controlled by the ratio of the feed MMA andstyrene. Limited conversion experiments should be able to control thecopolymerization to produce higher MMA incorporated copolymers. Smallamounts of amorphous polystyrene (a-PS) usually are obtained, presumablyfrom the product catalyzed by the incomplete reduced Ti^(IV) residue or{Cp*Ti^(III)(MMA)Me}⁺ complexes. This is confirmed by the observationthat the non-aged or non-Zn reduced Cp*TiMe₃/Ph₃C⁺B(C₆F₅)₄ ⁻-mediatedstyrene polymerization at room temperature produces large amounts ofa-PS. The reason for the atactic product may be that, compared with thevery open {Cp*TiMe}⁺ structure, the {Cp*Ti(X)Me}⁺ type complexes (X=Me,{Cp*Ti^(IV)Me₂}⁺ or X=MMA, {Cp*Ti ^(III)(η²-MMA)Me}⁺) is structurallytoo congested to adopt multiple styrene η⁴ coordination.

CP*Ti^(IV)Me₃ activated by a suitable cocatalyst has been extensivelystudied for styrene polymerization and is thought to be reduced to aTi^(III) species during aging. Without any reductant in the system butwith sufficient aging time, the Ti^(IV) species slowly undergo reductionto Ti^(III), indicated by a color change from red to dark brown or darkgreen and broadening of the Cp* ligand proton signals in the NMRspectra. Ti^(III) (d¹) species also are detected by ESR analysis. Thespecies, {Cp*Ti^(III)(PMe₃)₂Me}⁺, isolated from the addition of excessPMe₃ to the aged solution of Cp*TiMe₃/B(C₆F₅)₃ also has been observed.In the present experiments, the aging reduction of Ti^(IV) to Ti^(III)affords only low activity species for MMA polymerization (Comparison RunA). However, metallic Zn was found to accelerate such a reduction and,presumably, also to stabilize the low-valent species. The morecomplicated ¹H NMR spectrum of an aged catalyst solution compared tothat of a Zn-treated catalyst solution may be due to more rapiddecomposition of the catalyst in the absence of Zn. The catalyst afterZn treatment is more active for styrene and MMA homopolymerizations aswell as styrene/MMA copolymerization. Once a polymerization isinitiated, neither the rate nor polymer properties are sensitive to thepresence or absence or residual metallic Zn.

Either the PMMA or PS produced from homopolymerization is syndiotactic(Table 1, Ex. 1 and 2). Unlike radical, anionic, or cationiccopolymerizations that produce non-steroregulated random copolymers,i.e., copolymers consisting of all three possible styrene-MMA-styrene(or MMA-styrene-MMA) triad microstructures (co-sydio; co-hetero; andco-iso), the {Cp*Ti^(III)Me}⁺ mediated copolymerization of styrene withMMA using the catalyst systems of this invention typically producesmainly a co-iso random copolymer product, while a co-hetero structurehardly is detected. The MMA incorporation ratio is indicated by the PSortho-phenyl proton low field shift ratio (−δ 6.5 ppm for homo PS and ˜δ7.2 ppm for styrene/MMA copolymer) due to the interaction of PSortho-phenyl protons and PMMA ester groups.

Copolymers of vinyl aromatic monomers such as styrene and acrylatemonomers such as methyl methacrylate may be formed using the catalystsof this invention under typical polymerization conditions. Thesepolymeric materials include isotactic copolymers of styrene and MMA withMMA incorporation ranging from up to 2 to up to 30 mol percent or more.More particularly, these isotactic copolymers comprise from about 2 toabout 15 mol % of MMA and may contain about 4 to about 12 mol % MMA. Atypical isotactic copolymer of styrene and MMA of this inventioncontains about 10 mol % of MMA. Observation of an isotacticmicrostructure of these copolymers indicates substantial regions ofalternating styrene/MMA copolymer. Quantities of amorphous polystyrenealso may be combined with the styrene/MMA copolymer product of thisinvention.

Typical molecular weights of polymers of this invention may range fromabout 1000 to about 100,000 or above, and preferably are from about30,000 to about 90,000.

Fractions of polymer formed using the catalysts and techniques describedin this invention, may be separated by dissolving the total amount ofpolymer in a suitable solvent such as toluene and then selectivelyprecipitating fractions of polymer containing decreasing portions ofpolar monomer with a suitable antisolvent such as methanol.

This invention is illustrated, but not limited, by the followingexamples and comparative runs:

The catalyst precursors Cp*TiMe₃, Cp*TiMe₂, and Cp*TiCl₂, as well ascocatalysts B(C₆F₅)₃ and PBB were synthesized according to literatureprocedures. The starting materials Cp*TiCl₃, cocatalyst MAO, zinc, MMAmonomer and styrene monomer were obtained from Aldrich. The cocatalyst(C₆H₅)₃C⁺B(C₆F₅)₄ ⁻ was obtained from Asahi Glass Co. MMA and styrenewere purified by distillation from calcium hydride and stored at −30° C.over molecular sieves. Before polymerization experiments, AlEt₃ (Aldrichproduct) was added to the monomer or monomer mixture to make an 1×10⁻³ Msolution and aged for 10 min prior to vacuum transfer to the reactor todestroy protonic sources. Zn dust was washed with 10% HCl aqueoussolution, then with distilled water and acetone, and dried under vacuumovernight before transfer to a glovebox for storage. Solvents such astoluene or pentane were predried by storage over sodium wire thendistilled from and stored over Na/K alloy. Solid MAO was obtained byvacuum removal of solvent from the commercial 1.6 M hexane solution anddried under high vacuum (10⁻⁶ torr) overnight to remove AlR₃.(C₆H₅)₃C⁺B(C₆F₅)₄ ⁻ was purified by recrystallization fromtoluene/pentane.

EXAMPLE 1 Polymerization of Styrene Catalyzed by an In Situ GeneratedTi(III) Catalyst

A portion of dry styrene (2.0 milliliters (mL), 19 mmol) was vacuumtransferred into a 50 mL flame-dried oxygen-free, moisture-free flaskhaving a side outlet fitted with a rubber septum and equipped with amagnetic stirrer and was placed in a 21° C. water bath. A 2 mL Wilmadscrew-capped vial and an air-tight syringe were brought into a gloveboxand 7.0 mg (31 μmol) of Cp*TiMe₃, 28.0 mg (31.0 μmol) of(C₆F₅)₃C⁺B(C₆F₅)₄ ⁻, and about 1 mL of toluene was charged into thevial, followed by vigorous shaking for 2 minutes to allow the reagentsto react. Then 15 mg (225 μmol) of Zn powder was added to the solutionand the mixture allowed to stand for 75 min. The solution color changedfrom orange to dark brownish-green. The solution was removed from theglovebox and the supernatant injected into the stirring styrene solutionby syringe. After vigorously stirring for 15 min, the reaction wasquenched by addition of 20 mL of methanol (MeOH). The resulting polymerwas collected by filtration and then redissolved in 20 mL of C₂H₂Cl₄ at90° C. After addition of 100 mL MeOH to precipitate the polymer, thesuspension was filtered to remove any catalyst residue. The colorlesspolymeric material was then triturated with 100 mL of MeOH by vigorouslystirring for 24 h. The solid polymer was then collected by filtration,washed three times with 10 mL portions of MeOH, and dried at 120° C.under vacuum for 24 hours. The yield was 1.2 grams. Results are shown inTable 1.

EXAMPLE 2 Polymerization of MMA Catalyzed by an In Situ GeneratedTi(III) Catalyst

A portion of dry methylmethacrylate (MMA) (2.0 milliliters (mL), 19mmol) was vacuum transferred to a 50 mL flame-dried oxygen-free,moisture-free flask having a side outlet fitted with a rubber septum andequipped with a magnetic stirrer and was placed in a 21° C. water bath.A 2 mL Wilmad screw-capped vial and an air-tight syringe were broughtinto a glovebox and 7.0 mg (31 μmol) of Cp*TiMe₃, 26.0 mg (29.0 μmol) of(C₆F₅)₃C+B(C₆F₅)₄ ⁻, and about 1 mL of toluene was charged into thevial, followed by vigorous shaking for 2 min to allow the reagents toreact. Slightly less (C₆H₅)₃C⁺ B(C₆F₅)₄ ⁻ than Cp*TiMe₃ in molar ratiowas used to ensure complete reaction of (C₆H₅)₃C+B(C₆F₅)₄— and toeliminate possible cationic polymerization initiated by (C₆H₅)₃C⁺. Then,15 mg (225 μmol) of Zn powder was added to the solution and the mixtureallowed to stand for 80 min. The solution color changed from orange todark brownish-green. The solution was removed from the glovebox and thesupernatant injected into the stirring MMA solution by syringe. Aftervigorously stirring for 5 min, the reaction was quenched by addition of20 mL of MeOH. The resulting polymer was collected by filtration andthen redissolved in 20 mL CHCl₃. After addition of 100 mL MeOH toprecipitate the polymer, the suspension was filtered to remove anycatalyst residue. The colorless polymeric material was then trituratedwith 100 mL of MeOH by vigorously stirring for 24 hours. The solidpolymer was collected by filtration, washed three times with 10 mLportions of MeOH, and dried at 120° C. under vacuum for 24 h. The yieldwas 1.4 g. Results are shown in Table 1.

Comparative Run A Copolymerization of Styrene with MMA Catalyzed by anIn Situ Generated Ti(III) Species without Zn Assisted Reduction

In a glovebox, a 50 mL flame-dried oxygen-free, moisture-free flaskhaving a side outlet fitted with a rubber septum and equipped with amagnetic stirrer was charged with 10.3 mg (45.1 μmol) of Cp*TiMe₃, 40.1mg (43.5 μmol) of (C₆H₅)₃C⁺B(C₆F₅)₄ ⁻, and 2 mL of dry toluene. Theflask was placed in a 65° C. water bath for 30 min. The solution colorchanged from orange to brown. Then the flask was placed in another 2° C.water bath for 15 min to reach thermal equilibrium. Next, 10 mL (94mmol) dry 1:1 molar MMA/styrene mixture were injected into the stirringcatalyst solution by syringe. After 24 hours, the reaction was quenchedby addition of 20 mL MeOH and volatiles removed under vacuum. The solidpolymeric material was redissolved in 5 mL CHCl₃ and 50 mL of MeOH wasadded to precipitate the polymer. Colorless polymer was obtained byfiltration, triturated with 10 mL MeOH by vigorously stirring for 24 h.The solid polymer is then collected by filtration, washed with 3×5 mL ofMeOH, and dried at 120° C. under vacuum for 24 h. The yield was 0.8 g.Results are shown in Table 1.

EXAMPLE 3 Copolymerization of Styrene with MMA Catalyzed by In SituGeneration of Ti(III) Species with Zn Assisted Reduction

In a glovebox, a 50 mL flame-dried oxygen-free, moisture-free flaskhaving a side outlet fitted with a rubber septum and equipped with amagnetic stirrer was charged with 7.7 mg (34 μmol) of Cp*TiMe₃, 26.8 mg(29 μmol) of (C₆H₅)₃C⁺B(C₆F₅)₄ ⁻, and 1 mL of dry toluene. After 2 minwith occasionally shaking, 15 mg Zn powder was added to the flask. Theflask was placed in a 55° C. water bath and stirred for 25 min. Thesolution color changed from orange to brownish-green. Then the flask wasplaced in another 21° C. water bath for 15 min to reach thermalequilibrium. A portion (10 mL, 94 mmol) of dry 1:1 molar MMA/styrenemixture was injected into the stirring catalyst solution by syringe.After 180 min, the reaction was quenched by addition of 20 mL MeOH andvolatiles removed under vacuum. The solid polymeric material (6 g) wasextracted with a 1:3 toluene/MeOH mixture. This was carried out bydissolving the polymer in 100 mL toluene and then adding 300 mL MeOH.Copolymer with a higher proportion of incorporated MMA is more solublein toluene/MeOH mixture. The filtrate from the first extraction thuscontained 0.3 g of copolymer with about 36% MMA incorporation. The MMAincorporation ratio decreased with increasing numbers of extractions.The extraction was repeated three times, and the final product was foundto be a copolymer with about 15% MMA incorporation. The colorlesspolymeric material after extraction was obtained by removal of solventand then triturating with 100 mL MeOH by vigorously stirring for 24hours. The solid polymer was collected by filtration, washed with 3×10mL of MeOH, and dried at 120° C. under vacuum for 24 h. The yield was5.0 g. Results are shown in Table 1.

EXAMPLE 4 Copolymerization of Styrene with MMA Catalyzed by In SituGeneration of Ti(III) Species with Zn Assisted Reduction

Dry 20:1 styrene/MMA mixture (10 mL, 94 mmol) was vacuum transferredinto a 50 mL flame-dried, oxygen/moisture-free flask having a sideoutlet fitted with a rubber septum and equipped with a magnetic stirrer.The flask was placed in a 21° C. water bath. A 2 mL Wilmad screw-cappedvial and an air-tight syringe were brought into the glovebox. Next, 8.0mg (34 μmol) of Cp*TiMe₃, 30.0 mg (32.5 μmol) of (C₆H₅)₃C⁺B(C₆F₅)₄ ⁻,and about 1 mL of toluene were charged in the vial, followed by vigorousshaking for 2 min to allow the reagents to react. Then 25 mg (380 μmol)of Zn powder were added to the solution and the mixture aged for 1.5hours. Over this time period, the solution color changed from orange todark brownish-green. The solution was removed from the glovebox and thesupernatant injected into the stirring MMA/styrene mixture by syringe.After vigorous stirring for 60 min, the reaction was quenched byaddition of 20 mL of MeOH. After filtration, the polymer was extractedwith a 1:3 toluene/MeOH mixture, which was carried out by dissolving thepolymer in 100 mL toluene and then adding 300 mL MeOH. The filtrate fromthe first extraction contained 2 g (not dry) copolymer with about 40%MMA incorporation. The MMA incorporation ratio decreased with increasingnumbers of extractions. The extraction was repeated three times, and thefinal product was found to be a mixture of amorphous polystyrene (a-PS)and copolymer with about 10% MMA incorporation. Total yield of thecopolymer with about 9% MMA incorporation, according to thechromatography result, was 3.3 g. Results are shown in Table 1. The a-PSand copolymer in the mixture were separated by silica gel columnchromatography. TLC was used to determine the best solvent mixture aselutant. A 5:13 mixture of THF:pentane was found to be the best solventfor the separation of the a-PS/copolymer mixture. A 5 cm×20 cm silicagel column was used for chromatography, with 0.3 g of the polymermixture eluted by a solvent mixture of 100 mL of THF and 260 mL pentane.The column was finally eluted with 90 mL THF. All elutants werecollected in tubes (about 25 mL in each of 19 test tubes). Polymer wasdetected in the third, fourth, 16^(th), 17^(th), and 18^(th) test tubes.Removal of solvent from test tubes No. 8-10 afforded no polymer. ¹H NMRanalysis indicated that test tubes No. 3-4 contained copolymer and testtubes No.16-18 contained amorphous polystyrene homopolymer. Colorlesspolymeric material was obtained by removal of solvent and thentriturated in 4 mL MeOH by vigorously stirring for 24 h. The solidpolymer was collected by filtration, washed with 3×4 mL of MeOH, anddried at 120° C. under vacuum for 24 h. 0.2 g copolymer was obtained.The yield after extraction (containing both a-PS and copolymer) was 5.0g.

EXAMPLE 5 Copolymerization of Styrene with MMA Catalyzed by an In SituGenerated Ti(III) Species with Zn Assisted Reduction

Dry 20:1 styrene/MMA mixture 20 mL (188 mmol) was vacuum transferredinto a 50 mL flame-dried, oxygen/moisture-free flask having a sideoutlet fitted with a rubber septum and equipped with a magnetic stirrer.The flask was placed in a 60° C. water bath. A 2 mL Wilmad screw-cappedvial and an air-tight syringe were brought into the glovebox. Next, 8.0mg (34 μmol) of Cp*TiMe₃, 30.0 mg (32.5 μmol) of (C₆H₅)₃C⁺B(C₆F₅)₄ ⁻,and about 1 mL of toluene were charged in the vial, followed by vigorousshaking for 2 min to allow the reagents to react. Then 25 mg (385 μmol)of Zn powder were added to the solution and the mixture aged for 1.5 h.Over this time period, the solution color changed from orange to darkbrownish-green. The solution was removed from the glovebox and thesupernatant injected into the stirring MMA/styrene mixture by syringe.The solution became viscous after 15 min. After vigorous stirring for 60min, the reaction was quenched by addition of 20 mL of MeOH. Afterfiltration, the polymer was extracted with a 1:3 toluene/MeOH mixture.This was carried out by dissolving the polymer in 150 mL toluene andthen adding 350 mL MeOH. The filtrate from the first extractioncontained 4 g (not dry) copolymer with about 35% MMA incorporation. TheMMA incorporation ratio decreased with increasing numbers ofextractions. The extraction was repeated three times. The final productwas found to be a mixture of a-PS and copolymer with about 10% MMAincorporation. The yield after extraction was 5.5 g. Total yield of thecopolymer with about 10% MMA incorporation, according to thechromatography result, was 3.7 g. Results are shown in Table 1.

EXAMPLES 6-8

Further polymerizations of styrene and MMA were performed usingtechniques similar to those described for Example 3. The results areshown in Table 2.

EXAMPLES 9-11

Further polymerizations of styrene and MMA were performed usingtechniques similar to those described for Examples 4-5. In Examples9-11, a dry 19:1 styrene/MMA mixture (10.0 mL; 94 mmol) was used, andthe catalyst was prepared using 7.0 mg (31 μmol) of Cp*TiMe₃, 26 mg (29μmol) of Ph₃C⁺B(C₆F₅)₄ ⁻, 15 mg (225 μmol) Zn in 50 mL of toluene and 2hours reduction time. The results are shown in Table 2.

Comparative Runs B-E

A series of Comparative Runs were performed to confirm that the identityof the titanium-containing catalytic species. Four attemptedpolymerizations were conducted combinations of zinc power, dimethylzinc, and tritylperfluorophenyl borate as catalyst materials usingpolymerization techniques described in Example 1. Results are presentedin Table 3 and indicate the polymerization catalytic species observed inthe Examples is the Ti-containing species and not Zn or a borate. TABLE1 Example (Run) Ex. 1 Ex. 2 Run A Ex. 3 Ex. 4 Ex. 5 S:M¹ 1:0 0:1 1:1 1:120:1 20:1 (mol:mol) Feed Vol. 2.0 2.0 10.0 10.0 10.0 20.0 (mL) Temp. 2121 21 21 21 60 (° C.) Time 15 5 1440 180 60 60⁹ (min.) Y1² 1.2 1.4 0.86.0 8.0 18 (grams) Y1 MMA — — 10 — — — Content³ (% MMA) Y2⁴ — — — 5.05.0  5.5 (grams) Y2 MMA — — — 15 10 10 Content⁵ (% MMA) Y3⁶ — — — — 3.3 3.7 (grams) Y3 MMA — — — — 9 10 Content⁷ (% MMA) Tacticity s (>95%)s(80% rr) s/(co-iso + s) s/(co-iso + s) a-PS/co-iso a-PS/co-iso (S/M)⁸Mw 170 190 — 24.2 24.0 15.0 (×10⁻³) Mw/Mn 2.1 2.2 — 3.2 6.4  5.6¹S:M = Styrene:MMA ratio;²Yield after methanol precipitation from toluene polymer solution;³MMA content (mol. %) in the Y1 product;⁴Yield of product three times extracted with toluene/MeOH;⁵MMA content (mol. %) in the Y2 product;⁶Yield of chromatographically separated product;⁷MMA content (mol. %) in the Y3 product;⁸Tacticity determined by ¹³C NMR by measuring rr, rm and mm triads; s =syndiotactic (rr triads); co-iso = isotactic copolymer; a-PS = atacticpolystyrene;⁹Reaction probably completed in less time than stated, since productbecame viscous after 15 min.

TABLE 2 Example (Run) Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 S:M¹ 9:1 9:19:1 19:1 19:1 19:1 (mol:mol) Feed Vol. 10.0 10.0 10.0 20.0 20.0 20.0(mL) Temp. 21 21 21 0 21 50 (° C.) Time 10 20 30 720 720 720 (min.) Y1²3.0 3.2 3.0 8.9 12.7 12.0 (grams) Y1 MMA 10 9 10 — — — Content³ (% MMA)Y2⁴ — — — 8.0 11.5 11.0 (grams) Y2 MMA — — — 2.2 4.0 0.4 Content⁵ (%MMA) Y3⁶ — — — 0.4 1.1 0.6 (grams) Y3 MMA — — — 7.0 10 6.0 Content⁷ (%MMA) Tacticity s/co-iso s/co-iso s/co-iso co-iso co-iso co-iso (S/M)⁸ Mw31.3 33.1 92.5 — 1.3⁹ 1.5⁹ (×10⁻³) Mw/Mn 3.2 2.3 3.1 — 1.5⁹ 1.7⁹¹S:M = Styrene:MMA ratio;²Yield after methanol precipitation from toluene polymer solution;³MMA content (mol. %) in the Y1 product;⁴Yield of product three times unextracted with toluene/MeOH;⁵MMA content (mol. %) in the Y2 product;⁶Yield of chromatographically separated product;⁷MMA content (mol. %) in the Y3 product;⁸Tacticity determined by ¹³C NMR by measuring rr, rm and mm triads; s =syndiotactic (rr triads); co-iso = isotactic copolymer (mm triads);⁹Based on chromatographically separated portion.

TABLE 3 Run B C D E Catalyst Ph₃C⁺B(C₆F₅)₄ ⁻Zn Me₂Zn Ph₃C⁺B(C₆F₅)₄⁻Me₂Zn Ph₃C⁺B(C₆F₅)₄ ⁻Me₂Zn Amount of 41 200  28 28 Catalysts 122  200 200  (μmol) Monomers MMA (0.4) Styrene (19) Styrene (19) MMA (2) AmountsMMA (1) MMA (1) (mL) Temp. 21 21 21 21 ° C. Time 72 12 12 12 (hours)Results No Reaction Formed 0.41 g Formed 1.1 g of No Reaction ofamorphous copolymer polystyrene containing 2.5% MMA

1-32. (canceled)
 33. A method of polymerizing olefins comprisingcontacting one or more olefin monomers under polymerization conditionswith a catalyst formed by in situ reduction of a catalyst precursorcomprising.{Cp*MRR_(n)′}⁺{A}⁻ wherein CP* is a cyclopentadienyl or substitutedcyclopentadienyl moiety; M is an early transition metal; R is a C₁-C₂₀hydrocarbyl; R′ is independently selected from hydride and C₁-C₂₀hydrocarbyl; n is an integer selected to balance the oxidation state ofM; and A is a suitable non-coordinating anionic cocatalyst, with areducing agent.
 34. A method of polymerizing olefins comprisingcontacting one or more olefin monomers under polymerization conditionswith a catalyst formed by in situ reduction of a catalyst precursorcomprising{Cp*MRR_(n)′}⁺{A}⁻ wherein Cp* is a cyclopentadienyl or substitutedcyclopentadienyl moiety; M is a Group 4 transition metal; R is a C₁-C₂₀hydrocarbyl; R′ is independently selected from hydride, C₁-C₂₀hydrocarbyl n is 0 or 1 selected to balance the oxidation state of M;and A is a suitable non-coordinating anionic cocatalyst, with a metallicreducing agent. 35-37. (canceled)
 38. The method of claim 33 using acatalyst system in which the transition metal is a Group 4 transitionmetal.
 39. The method of claim 33 using a catalyst system in which thetransition metal is titanium and the Cp* is cyclopentadienyl.
 40. Themethod of claim 33 using a catalyst system in which R and R′ are C₁-C₂₀alkyl, aryl, alkylaryl or arylalkyl groups.
 41. The method of claim 33using a catalyst system in which the reducing agent is a metal or metalalloy.
 42. The method of claim 33 using a catalyst system in which thereducing agent is zinc.
 43. The method of claim 33 using a catalystsystem in which A is a perfluroaryl borate.
 44. The method of claim 33using a catalyst system in which A is derived from a borane cocatalystprecursor.
 45. The method of claim 33 using a catalyst system in whichthe cocatalyst precursor is tris(pentafluorophenyl)borane;tris(2,2′,2″-nonafluorbiphenyl)borane; ortris(β-perfluoronaphthyl)borane.
 46. The method of claim 33 using acatalyst system in which the cocatalyst precursor istris(2,2′,2″-nonafluorbiphenyl)borane.
 47. The method of claim 34 usinga catalyst system in which M is Ti^(IV) and n=1.
 48. The method of claim47 using a catalyst system in which R and R′ are C₁-C₄ alkyl groups andin which Cp* is cyclopentadienyl.
 49. The method of claim 48 using acatalyst system in which R and R′ are methyl groups.
 50. The method ofclaim 48 in which a polymerized monomer comprises C₂ to C₂₀ polarmonomers containing an olefinic group.
 51. The method of claim 48 usinga catalyst system in which the cocatalyst precursor istris(pentafluorophenyl)borane; tris(2,2′,2″-nonafluorbiphenyl)borane; ortris(β-perfluoronaphthyl)borane.
 52. The method of claim 50 in which apolar monomer comprises unsaturated acids and their derivatives, vinylesters, vinyl amides, vinyl amines, and acrylonitrile.
 53. The method ofclaim 48 in which a polymerized monomer comprises C₂ to C₂₀ nonpolarmonomer containing an olefinic group.
 54. The method of claim 53 inwhich a polymerized olefin monomer comprises styrene.
 55. The method ofclaim 52 in which a polymerized olefin monomer comprises methylmethacrylate.